/*
 * This project provides a number of implementations for indexing and evaluating
 * <i>Continuous Top-k Queries over Text Streams</i>
 * and has been developped as part of the work described in the article:
 * 
 * Vouzoukidou, N., Amann, B., & Christophides, V. (2012, October). 
 * Processing continuous text queries featuring non-homogeneous scoring functions.
 * In Proceedings of the 21st ACM international conference on Information and 
 * knowledge management (pp. 1065-1074). ACM.
 * http://dl.acm.org/citation.cfm?id=2398404
 * 
 * This software is distributed under the GNU General Public License and as an
 * additional condition of usage, please cite the aforementioned article.
 * 
 * Copyright (C) 2012 ICS/FORTH, Greece and 
 *               2012 LIP6, France
 * 
 * Author: Vouzoukidou Nelly, email: nelly.vouzoukidou (at) gmail (dot) com
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package gr.forth.ics.continuoustopk;

import java.util.HashMap;
import java.util.Map;

/**
 * Represents a term of the query or item vocabulary. 
 * 
 * <p>No public constructor is provded. Instead the {@link #newTerm(java.lang.String)}
 * method creates and retruns new instances of this class, while also making sure
 * that no duplicates are created: Two instances of Term are equal when object equality
 * is true.</p>
 *
 * @author Vouzoukidou Nelly, email: nelly.vouzoukidou (at) gmail (dot) com
 */
public class Term implements Comparable<Term> {
    private String term;

    private static Map<String, Term> terms = new HashMap<String, Term>();

    /** 
     * A static constructor of terms. Creates and returns a new object only if 
     * not already existing or returns the old value if it already exists.
     * 
     * @param term the string representation of the required term
     * @return a Term object with the given term
     */
    public static Term newTerm(String term) {
        Term value = terms.get(term);
        if (value == null) {
            value = new Term(term);
            terms.put(term, value);
        }
        return value;
    }

    private Term(String term) {
        this.term = term;
    }

    /**
     * Returns the String representation of this term.
     * @return the String representation of this term.
     */
    public String term() {
        return term;
    }

    @Override
    public boolean equals(Object other) {
        if (!(other instanceof Term)) {
            return false;
        }
        // no need to optimize by checking obejct equality: if they are equal
        // they will have the same String term object
        return this.term.equals(((Term)other).term);
    }

    @Override
    public int hashCode() {
        return term.hashCode();
    }

    @Override
    public String toString() {
        return term;
    }

    @Override
    public int compareTo(Term term) {
        return this.term.compareTo(term.term);
    }
}
